Atherosclerotic coronary vascular disease is the leading cause of death in the world. The endothelium which lines the coronary and peripheral vascular arteries is responsible for maintaining vascular tone, preventing thrombosis, and vascular integrity. Early atherosclerosis, prior to significant invisible stenosis, is characterized by endothelial dysfunction. Patients with risk factors for atherosclerosis have been shown to have abnormal endothelial function. Non-insulin dependent diabetes mellitus (NIDDM) affects over 18 million Americans and is associated with accelerated atherosclerosis of large vessels. The vascular pathology begins well before the onset of hyperglycemia and is strongly associated with insulin resistance (IR) which precedes the clinical onset of NIDDM. Obese people have a high incidence of IR. Obese people with IR and without other risk factors for endothelial dysfunction have been shown to have abnormal endothelial function in their femoral arteries. The specific aim of this study is to evaluate coronary endothelial function in insulin sensitive and obese/insulin resistant people. We theorize that IR, independent of other risk factors, is associated with abnormal coronary endothelial function.